Strain Relief for Connector and Cable Interconnection

ABSTRACT

A strain relief for a coaxial cable and coaxial connector interconnection is provided as an injection moldable polymer material surrounding the interconnection. The injection moldable material fills a solder pre-form cavity between an outer conductor of the coaxial cable and an inner diameter of a bore of the connector body, strengthening and environmentally sealing the interconnection. Where the outer conductor is corrugated, the polymer material may be provided covering an exposed portion of the corrugations and/or filling portions of a corrugation trough between an outer jacket and the outer diameter of the outer conductor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a strain relief for a coaxial RF connector.More specifically, the invention relates to a strain relief moldableabout a corrugated outer conductor cable to connector interconnection,providing sealing and strength characteristics which enhance the coaxialconnector to coaxial cable interconnection.

2. Description of Related Art

Coaxial cables and coaxial connectors are used, for example, incommunication systems requiring a high level of precision andreliability. To create a cost efficient electro-mechanicalinterconnection between the coaxial cable and the coaxial connector, itis often desirable to interconnect the cable and connector viasoldering.

Solder pre-forms may be utilized to improve interconnection quality whensoldering coaxial connectors to coaxial cables. The use of a solderpre-form standardizes the location and amount of solder applied.Representative of this technology is commonly owned U.S. Pat. No.5,802,710 issued Sep. 8, 1998 to Bufanda et al (Bufanda). Bufandadiscloses a solder pre-form with a planar connector side (outer surface)and a cable side (inner surface) dimensioned to key with corrugations ofan annular corrugated outer conductor. Other solder pre-forms, forexample for soldering a coaxial connector with a smooth sidewall outerconductor coaxial cable, have been provided as a plurality of annularrings and/or a cylindrical tube. For ease of assembly prior tosoldering, the solder pre-forms typically fit loosely within a desiredinterconnection area solder cavity formed between the connector body andthe outer conductor.

Connector to cable interconnection soldering is typically performed withthe connector and coaxial cable vertically oriented, for example asdisclosed in U.S. Pat. No. 7,900,344 issued Mar. 8, 2011 to Ng, et al.Thereby, when heat is applied to the solder pre-form during the solderprocess, the solder liquefies and pools in the bottom of theinterconnection area solder cavity. The solder pooling leaves an annularsolder pre-form cavity between the outer conductor and the connectorbody that extends to the cable end of the connector body.

Coaxial cables may utilize aluminum material, for example to realize acost of materials and/or weight savings advantage. However, use ofaluminum may also introduce the disadvantages of reduced strength and/orbending resilience. Aluminum material exposed to air quickly oxidizes,forming an aluminum oxide coating that interferes with solder bonding.Special aluminum material specific soldering flux with a heat activatedhigh acid content may be used to prepare aluminum material surfaces forsoldering. However, such flux may be difficult to apply evenly withinthe interconnection area.

Heat shrink tubing has been utilized as a cosmetic and/or strain reliefimprovement for connector to coaxial cable terminations. However, heatshrink tubing may provide only a limited environmental seal that mayallow moisture ingress/condensation which then pools under the heatshrink tubing, directly upon the interconnection.

Therefore, it is an object of the invention to provide an apparatus andmethod of manufacture that overcomes deficiencies in such prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a schematic partial cut-away view of a coaxial connector tocoaxial cable solder interconnection.

FIG. 2 is a schematic partial cut-away side view of the coaxialconnector to coaxial cable solder interconnection of FIG. 1 with anexemplary strain relief applied.

FIG. 3 is a schematic isometric view of FIG. 2, with a partial cut-awayportion to clarify details of the strain relief.

FIG. 4 is a close-up of area A of FIG. 3.

FIG. 5 is a schematic isometric cut-away end view of the coaxialconnector to coaxial cable solder interconnection of FIG. 2,demonstrating a partial cross section of the interconnection area, withthe connector body removed for clarity of understanding potential cavityand/or channel defects of the solder joint.

FIG. 6 is a schematic isometric view of the connector body of thecoaxial connector of FIG. 1.

FIG. 7 is a schematic isometric cut-away view of a coaxial connector toannular corrugated coaxial cable solder interconnection.

FIG. 8 is a close-up of area D of FIG. 7.

FIG. 9 is a schematic isometric cut-away view of a coaxial connector tohelical corrugated coaxial cable solder interconnection.

FIG. 10 is a close-up of area B of FIG. 9.

FIG. 11 is an isometric view of the interconnection of FIG. 7.

DETAILED DESCRIPTION

The inventor has recognized that solder interconnections between coaxialconnectors and coaxial cables, particularly where coaxial cables withaluminum material outer conductors are utilized, may have significantstrength deficiencies due to the relative strength and resilience ofaluminum outer conductors compared to the prior copper material outerconductors. Further, because the specialized flux used in preparationfor soldering aluminum material is difficult to apply smoothly, anexcess of flux may be applied, resulting in flux residue at thecompletion of the solder operation that then requires additional stepsto remove, where possible.

The residue of flux may be merged within the solder joint in the form ofchannels and/or cavities, making removal of all flux residue,particularly from the immediate area of the solder joint, impracticaland/or impossible. The inventor has further recognized that this fluxmay also be hygroscopic and increasingly corrosive as water is absorbed.

The inventor has created a strain relief for coaxial connectors whichimproves both the overall strength of the joint and the seal sealingproperties of the strain relief upon the interconnection.

As shown in FIG. 1, an interconnection between an exemplary coaxialconnector 1 and a coaxial cable 3 utilizes a solder joint 2 between theouter diameter of the outer conductor 4 and an inner diameter of aninterconnection area 6 of the bore 8 of a connector body 10. Adielectric disc 12 may be applied to close the connector end of theinterconnection area 6, thereby reducing the chance of molten solderegress from the connection area 6. As the solder pre-form melts andpools, an annular pre-form cavity 14 is formed between the resultingsolder joint 2, inner diameter of the bore 8, outer diameter of theouter conductor 4 and a cable end of the connector body 10.

A strain relief 16 for the coaxial cable and coaxial connectorinterconnection may be formed by injection molding a polymer material tosurround the interconnection with at least one contiguous polymerportion 18, for example as shown in FIG. 2.

The polymer material may be a thermoplastic material suitable for lowtemperature, low pressure injection molding, with resilientcharacteristics that is ultra-violet resistant and weatherproof. Asuitable polymer material is polyamide; an exemplary polyamide materialis Macromelt® OM 648, available from Henkel AG & Co.KGaA of Dusseldorf,Germany. Alternatively, any suitable low pressure injection moldedthermoplastic adhesive may be applied.

Low pressure injection molding may provide suitable cavity penetration,without otherwise damaging the existing coaxial cable and/orinterconnection. A preferred pressure range for the low pressureinjection molding is between 5 and 40 bar. Similarly, the heat of theinjection molding should be low enough to avoid softening the solderjoint, damaging the polymer insulation and/or outer jacket 20 of thecoaxial cable 3. A preferred temperature range of the injection moldingis between 200 and 240 degrees Celsius. Alternatively, where thepressure and temperature of standard injection molding may be appliedwithout damage to the cable and/or interconnection, such may also beapplied.

The liquid injection of the polymer material during the injectionmolding fills the pre-form cavity 14, and seals against the connectorbody 10 and outer jacket 20, encapsulating any remaining flux and/orfurther filing any voids, channels 21 and/or cavities 23 that may bepresent in the solder joint, for example as shown in FIGS. 3-5. Thereby,the solder joint 2 and any flux residue is entirely encapsulated frommoisture ingress that may corrode the metal surfaces and/or react withthe flux residue to initiate accelerated corrosion of the metal surfacesand/or solder joint.

As best shown in FIG. 2, the strain relief 16 may be shaped to a desiredcoverage area, thickness and/or external surface configuration by themold that is applied around the interconnection during the injectionmolding.

The strain relief 16 may be anchored upon a strain relief portion 22 ofthe connector body 10 of the coaxial connector 1. The strain reliefportion 22 may be provided with a plurality of retention features, suchas grooves, protrusions or the like. As best shown in FIG. 6, where theretention features are non-cylindrical, such as raised segments 24, ananti-rotation characteristic is provided which further increases theseal and/or retention of the strain relief 16 upon the strain reliefportion 22. The strain relief portion 22 may be provided adjacent to atool face portion 26 of the connector body provided with tool faces forreceiving a hand tool or the like to hold the connector stationary as acoupling nut is threaded during interconnection of the connector withanother connector and/or device. One skilled in the art will appreciatethat where the raised segments 24 and tool face portion 26 are appliedwith a common geometry, anti-rotation benefits of the raised segments 24are realized and machining of the connector body 10 may be simplified.

The strain relief 16 may have a cable portion 28 extending over thecoaxial cable 3 which tapers toward the cable end, providingreinforcement to the interconnection which also tapers, such that thereinforcement provided by the strain relief 16 does not abruptlyterminate at a rigid edge where the coaxial cable 3 would likely buckleif subjected to excess bending forces near the interconnection.

A cable portion 28 of the strain relief 16 may extend away from theinterconnection over the coaxial cable 3 a significant length, such as adistance greater than three diameters of the coaxial cable 3.

In addition to and/or instead of a taper applied to the cable portion28, the cable portion 28 may be provided with a plurality of stressrelief grooves 30. The stress relief grooves 30 may be applied asgenerally elliptical grooves with a major axis of the stress reliefgrooves 30 arranged normal to a longitudinal axis of the coaxialconnector 3. A spacing, width and/or depth of the stress relief grooves30 may be adjusted to progressively reduce a bending resistance towardthe cable end, further enhancing a tapered support characteristic, whichwhile significantly increasing the strength of the interconnection, alsoprotects the coaxial cable 3 from buckling proximate the end of thestrain relief 16 due to any excess bending forces that may be applied,thereby increasing both the overall strength and the flexibilitycharacteristics of the interconnection.

The strain relief 16 may alternatively be applied to coaxial cables 3with corrugated outer conductors 4, including coaxial cables 3 withconductors of conventional metals, such as copper.

Where the corrugations 32 are annular, for example as shown in FIGS. 7and 8, or helical, a portion of the outer jacket 20 may be stripped backto expose a portion of the outer conductor 4 between the connector body10 and the outer jacket 20, along a longitudinal axis of the coaxialcable 3 and the polymer material applied covering the exposed portion 36of the outer conductor 4. The exposed portion 36 may extend, along alongitudinal axis of the coaxial cable, for at least two trough-peakcorrugations. That is, for a length containing at least two peaks and/ortwo troughs.

In this embodiment, instead of providing the polymer material sealingprimarily against the outer jacket 20, an extended area of directcontact with the outer conductor 4 is provided along which the polymermaterial may directly interlock with the outer conductor 4, keyed to theouter conductor by the corrugation troughs 32. Thereby, any elasticityof the outer jacket 20, in particular where it is extending acrosscorrugation troughs 34 of the outer conductor 4, and/or potential forthe outer conductor 4 to move longitudinally with respect to the outerjacket 20 may be eliminated from these portions of the strain relief 16.

Alternatively, as shown for example in FIGS. 9 and 10, where thecorrugations of the outer conductor 4 are helical, a continuouscorrugation trough 34 threads around and longitudinally along the outerdiameter of the outer conductor 4, between the outer conductor 4 and theouter jacket 20. During molding of the strain relief 16, the polymermaterial will enter the corrugation trough 32 where the outer jacket 20abuts the pre-form cavity 14 or at a further position along the outerconductor 4 which the outer jacket 20 may be stripped back towards. Theextent of polymer material fill along the corrugation trough 34 may becontrolled by adjusting the viscosity of the polymer material, forexample via formulation and/or temperature and/or the pressure appliedduring the injection molding. To provide a portion of supported outerjacket 20 with reduced elasticity characteristic similar to the exposedportion 36 described herein above, the corrugation trough 34 may befilled with the polymer material for at least one circumference of theouter conductor 4.

A corrugated outer conductor coaxial cable 3, particularly one utilizingconventional copper material, typically has a greater flexibilitycharacteristic and/or resistance to buckling. Therefore, the cableportion 28 of the strain relief 16 may be applied with a generallyshorter extent and/or thickness to conserve polymer material, forexample as shown in FIG. 11. Further, the strain relief 16 may beprovided with a streamlined configuration wherein an outer diameter ofthe polymer portion 18 is provided as generally cylindrical at aconnector end and a tapered cone at a cable end.

One skilled in the art will appreciate that a strain relief 16 accordingto the invention may improve connector body 10 to outer conductor 4interconnection strength and environmental seal. Thereby, prior concernsof flux residue contributing to accelerated degradation of theinterconnection quality and/or environmental sealing of a solder joint 2that may contain cavities and/or channels are reduced, especially wherealuminum materials are being utilized. Thereby, the further adoption ofaluminum material use in the coaxial connector and/or coaxial cable artsis enabled, which in turn may enable significant material cost savingsfor connector and coaxial cable manufacturers.

The strain relief 16 is also useful with non-aluminum conductor cables,such as annular or helical corrugated copper coaxial cable, as thepresence of a strain relief 16, in addition to reinforcing the strengthof the connector body 10 to outer conductor 4 interconnection, inhibitscable bending proximate the cable end. Thereby, conductor movements at aconnection interface of the coaxial connector 1 which may otherwisecontribute to the generation of passive inter-modulation distortion maybe reduced.

Table of Parts

1 coaxial connector 2 solder joint 3 coaxial cable 4 outer conductor 6interconnection area 8 bore 10 connector body 12 dielectric disc 14pre-form cavity 16 strain relief 18 polymer portion 20 outer jacket 21channel 22 strain relief portion 23 cavities 24 raised segment 26 toolface portion 28 cable portion 30 stress relief groove 32 corrugation 34corrugation trough 36 exposed portion

Where in the foregoing description reference has been made to ratios,integers or components having known equivalents then such equivalentsare herein incorporated as if individually set forth.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin considerable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, representativeapparatus, methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departurefrom the spirit or scope of applicant's general inventive concept.Further, it is to be appreciated that improvements and/or modificationsmay be made thereto without departing from the scope or spirit of thepresent invention as defined by the following claims.

We claim:
 1. A strain relief for a coaxial cable and coaxial connectorinterconnection, the coaxial cable provided with an outer conductor andthe coaxial connector provided with a connector body with a bore, thestrain relief comprising: an injection moldable polymer materialsurrounding the interconnection; the injection moldable polymer materialfilling a solder pre-form cavity between the outer conductor of thecoaxial cable and an inner diameter of the bore of the connector body.2. The strain relief of claim 1, wherein the outer conductor hascorrugations and a jacket of the coaxial cable, surrounding the outerconductor, is stripped back to expose a portion of the outer conductorbetween the connector body and the jacket, along a longitudinal axis ofthe coaxial cable; the injection moldable polymer material covering theexposed portion of the outer conductor.
 3. The strain relief of claim 2,wherein the corrugations are annular.
 4. The strain relief of claim 2,wherein the exposed portion extends, along a longitudinal axis of thecoaxial cable, for at least two trough-peak corrugations.
 5. The strainrelief of claim 1, wherein the outer conductor has helical corrugations;the injection moldable polymer material filling a helical corrugationtrough of the outer conductor, between the outer conductor and a jacketsurrounding the outer conductor, for at least one circumference of theouter conductor.
 6. The strain relief of claim 1, wherein an outerdiameter of the injection moldable polymer material is generallycylindrical at a connector end and a tapered cone at a cable end.
 7. Thestrain relief of claim 1, wherein the injection moldable polymermaterial is a polyamide material.
 8. The strain relief of claim 1,wherein the strain relief surrounding the coaxial connector is seatedupon a strain relief portion of the connector body.
 9. The strain reliefof claim 8, wherein the strain relief portion is provided with aplurality of non-cylindrical raised segments.
 10. The strain relief ofclaim 8, wherein the strain relief portion abuts a tool face portion ofthe connector body.
 11. A method for manufacturing a strain relief for acoaxial cable and coaxial connector interconnection, the coaxial cableprovided with an outer conductor and the coaxial connector provided witha connector body with a bore, the strain relief comprising the steps of:injection molding a polymer material around the interconnection; theinjection moldable material filling a solder pre-form cavity between theouter conductor of the coaxial cable and an inner diameter of the boreof the connector body.
 12. The method of claim 11, wherein the polymermaterial is a polyamide material.
 13. The method of claim 11, whereinthe injection moldable material is applied during the injection moldingat a temperature between 200 and 240 degrees Celsius.
 14. The method ofclaim 11, wherein the injection molding is performed with an injectionpressure between 5 and 40 bar.
 15. The method of claim 11, wherein theouter conductor has corrugations and a jacket of the coaxial cablesurrounding the outer conductor is stripped back to expose a portion ofthe outer conductor between the connector body and the jacket, along alongitudinal axis of the coaxial cable; the injection moldable polymermaterial covering the exposed portion of the outer conductor.
 16. Themethod of claim 15, wherein the corrugations are annular.
 17. The methodof claim 15, wherein the exposed portion extends, along a longitudinalaxis of the coaxial cable, for at least two trough-peak corrugations 18.The method of claim 11, wherein the outer conductor has helicalcorrugations and a jacket of the coaxial cable, surrounding the outerconductor; the injection moldable polymer material filing a helicalcorrugation trough of the outer conductor, between the outer conductorand the jacket, for at least one circumference of the outer conductor.19. The method of claim 18, wherein an injection pressure is applied,the injection pressure selected to fill a desired portion of the helicalcorrugation trough with the injection moldable polymer material.
 20. Themethod of claim 11, wherein an outer diameter of the injection moldablepolymer material is generally cylindrical proximate a connector end anda tapered cone proximate a cable end.